After an attempted prison breakout, one of the prisoners is killed, presumably by one of the guards. The prisoners riot and take over the prison, insisting on an in-prison trial for the guard. Matlock is recruited to defend the guard.
You threw me when you said it might be from a tv series. With prime time television censorship, the violence could not be very jarring and thus not that memorable.
There are some violent prison films which make those tv shows look rather tame.